Delivery by trypanosoma cruzi of proteins into mhc class i antigen processing and presentation pathway

Class I MHC-restricted T cell responses have been shown to be critical to the development of immune resistance in Trypanosoma cruzi infections in mice. However, the antigenic targets of this response have not been characterized. We analyzed the characteristics of potential 7. cruzi cytotoxic T lymphocyte (CTL) target molecules by expression of the model CTL target molecule ovalbumin (OVA) in different cellular compartments of the parasite. Incorporation of a cleavable signal sequence from glycoprotein 72 of T, cruzi or leader peptide of influenza hemagglutinin resulted in a truncated ovalbumin (139-385 amino acids) which was . rapidly secreted from transfected parasites. Replacement of secretory signal sequence with the signal/anchor domain of the human transferrin receptor resulted in the,transport of the molecule to the cell surface of transfected parasites without significant release. Ovalbumin given the N-termina! signal sequence of mouse interleukin-2 was neither secreted nor expressed on the cell surface and was presumably degraded inside the transfected parasites. Antigen presenting cells (APC) infected with parasites secreting OVA in the cytoplasm of host cells could process and present OVA, as indicated by the stimulation of OVA-specific CD8⁺T cell hybridomas. However, APC's infected with T. cruzi producing cytoplasmic or transmembrane forms of OVA did not present OVA via the MHC class I pathway. These results suggest that proteins secreted by T. cruzi in infected cells are the maior source of peptides for MHC class I presentation and for the generation of parasite-specific cytotoxic T lymphocytes.